Electric discharge lamp



June 22, 1943. r J L cox 2,322,421

' v ELECTRIC DISCHARGE LAMP Original Filed Dec. 22. 1938 "0/11/14 llIl/4 III/II 1111/ ATTOQNEY Patented June 22, 1943 James L. Cox,

Danvers,

Mass., assignor to Sylvania Electric Products Inc., a corporation of Massachusetts Original application December 22, 1938, Serial No. 247,252. Divided and this application April 8, 1942, Serial No. 438,199

2 Claims. (Cl. 116-7) This invention relates to electric gaseous discharge lamps, and inparticular to such lamps of the tubular type.

An object of the invention is to provide such lamps with a glass end cap directly sealed to the ends of the tube and through which metal contact prongs extend, thus obviating the necessity of cementing an external contact base on the end of the lamp.

Another object is to permit the placing of the electrodes in such a lamp close to the ends of the tube, in order that the discharge may appear to fill the entire length of the tube.

Still another object is to eliminate any pockets at the end of the tube, in which the mercury oiten used with such lamps might be trapped and kept out of the discharge.

A still further object is to provide a means of inserting an accurately inserted quantity of mercury in such a tube by the use of a metallic bomb; and yet another object is to facilitate starting of the tube.

Other objects and advantages will be apparent from a consideration of the following description, taken in connection with the accompanying drawing in which:

Figure 1 is a sectional elevation of a lamp according to the invention;

Figure 2 is an elevation taken from the end of the tube;

Figure 3 shows an enlarged lengthwise view, partly in section of the bomb used in the invention; and

Figure 4 is a transverse view of the same bomb;

Figure 5 is a side view, in section, of one form of a glass disc, before the wires are sealed through it;

Figure 6 is a front or plan view of the cathode with the bomb placed at the side of, instead of behind, the coiled electrode;

Figure 7 is a side view of the arrangement of Figure 6.

In Figure 1, an elongated glass tube I, has sealed to each of its ends a glass disc 2, 3, closing the tube. Stifi metal wires 4, 5 are sealed through the glass discs to act as supports for the electrodes 6, 1, inside the tube and as contact prongs outside the sealed envelope. An exhaust tube 8, is attached to at least one of the glass discs. The disc is preferably made concave as 3, so that the exhaust tube 8, can be sealed fiush with the ends of the tube as shown, although the disc may be made flat, as 2, in which case if an exhaust tube is used with it, the tube willextend out somewhat beyond the ends of the tube, and may be more easily subject to damage. The electrodes 6 I, may comprise a coiled tungsten wire, coated with one or more of the alkaline earth oxides; and is preferably arranged as a coiled-coil, in order to metal tube It of small diameter, of which each end I I, I2, is closed by being flattened or pressed together as shown, with a drop l8, of mercury of the desired quantity in the tubular portion of the bomb, between the flattened end portions. The mercury is thus roughly sealed into the bomb. One flattened end H, is welded or otherwise attached to one of the filament lead-in wires 4, as shown in Figure 1, preferably just behind the filament as shown, although it may be placed in front of the filament, that is in the path of the discharge, if desired; or at the side of the filament as in Figures 6, and 7. The mercury remains in the bomb while the lamp is being made and until the lamp is nearly completed. The filament is then brought to the proper temperature and the bomb is heated by it, until the pressure of the heated mercury rises sufiiciently to make an opening in the bomb. The mercury then escapes into the lamp atmosphere.

One end I L01 the bomb is preferably welded, or otherwise conductively connected to one lead I, of the filament, and the other end l2 of the bomb placed close to, but not in contact with, the other filament lead 5. Then when the heating current flows through the filament 4, the drop in voltage across the filament will be present across the small gap between the end l2, of the bomb and the lead 5, of the filament. If the filament voltage is greater than the ionizing voltage of the gas, or at least greater than the resonance potential, the gas in the gap will be excited and will aid in starting the are between the electrodes at each end of the tube.

In Figures 6 and 7, the bomb 9 is placed at the side of, and parallel to the filament l, but it still acts as a starting electrode in the manner just related. If the voltage between the bomb and any portion of the filament, rises to a voltage above the excitation potential of the gas, the discharge will begin between the portion of the filament above that voltage, and the bomb, and

and connected to the end of the filament oppo-.

site that to which the bomb is electrically connected.

Figure 2 can be clearly understood from the description of Figure l, and Figures 3 and 4 have been described above.

Figure 5 shows a glass disc before the wires are sealed through it. The disc is molded, and has holes i3, ll, for the wires 3, 4. Small hubs II, It, are placed around the holes to facilitate sealing the wires through the holes. The wires are placed through the holes and the hubs are heated by flames or by some other method to seal the glass to the metal. The disc shown in Figure 5, also has a slight annular hub H, on one side of its rim. This may be butted against the end of the tube I, and in register with it to facilitate sealing the disc to the tube. Such a hub is not essential, however, and the discs shown in Fig ure 1 do not employ it. Whether or not this hub is used, the end of the tube I and the rim of the disc are heated, butted together, and heated further until the glass softens to eifect a seal. The rim of the disc, and the end of the tube, may be heated by directing gas flames on them, or by placing a carbon ring around the region to be sealed and passing an electric current through the carbon to heat it and the glass.

A filling of one or more inert gases, such as argon at a pressure of 3 mm. of mercury or neon at 8 mm.,' will generally be present in the tube,

an alloy of iron containing 26% chromium may be used, or an alloy of 37% iron, 25% nickel, 30% cobalt, and 8% chromium.

If ultraviolet light is desired from the envelope, a substantially iron-tree borosilicate glass will prove satisfactory.

My glass disc construction enables the electrodes to be brought closer to the ends of the tube than is possible in a tube using the usual reentrant stems of the type common in the lamp industry. This eliminates the dark spaces behind the cathodes, and enables the light from the discharge to fill practically the entire length of the tube, which is especially advantageous if a fluorescent coating is placed on the inside of the tube.

This application is a division of my co-pending application Serial No. 247,252 filed December 22, 1938.

What I claim is:

l. The method of introducing mercury into a sealed glass envelope, said method comprising: introducing a quantity of mercury into a metal container; sealing said mercury in said container; mounting said container adjacent a filament mounted on a pair of filament leads secured in a glass end piece for said envelope, with one end of said container electrically connected with one of said filament leads and the other end of said container lying in adjacent and separated relation with the other of said filament leads; sealing said glass endpiece to the end of said glass envelope; and passing a current of electricity through said filament sufiicient to cause it to give off heat capable of causing such expansion of said mercury as will force an opening in said container.

2. The method of introducing mercury into a sealed glass envelope, said method comprising: introducing a quantity of mercury into a metal container; sealing said mercury in said container; mounting said container in unitary assembly with an end piece for said envelope and a filament mounted on a pair of filament leads secured in said end piece, with said container positioned within the effective heating range of said filament; sealing said endpiece to the end of said envelope; and passing a current of electricity through said filament suflicient to cause it to give off heat capable of causing such expansion of said mercury as will force an opening in said container.

JAMES L. COX. 

